The invention generally relates to a transmission assembly for use in manually powering a device such as a bicycle. More particularly, the invention concerns a multispeed, gear-driven transmission bicycle transmission having a broad range of gear ratios making it suitable for operation in a wide variety of terrains. Moreover, the transmission includes an eccentric cranking mechanism which ergonomically takes advantage of the cranking power available from an individual.
Bicycle driving mechanisms are, of course, known in the prior art. For example, U.S. Pat. No. 628,184 which issued to Plass concerns a bicycle driving mechanism having a multigear transmission casing mounted in a frame which is vertically movable in the casing between the crank shaft and a second shaft. An operating rod raises or lowers the frame to the require position. Transmission gear wheels are fixed to upper, central, and lower shafts that, in turn, are journaled between to bars of the first frame. Movement of the second frame engages the alternate driving gear wheels and imparts motion to the mechanism.
It is also known to employ multiple gears of various diameters mounted on a frame in a bicycle transmission. A lever mounted on the frame carries a gear adapted to mesh with the gears of the pedal shaft. Multiple gears mounted on the frame transmit movement of the pedal shaft to the multiple gears mounted on an auxiliary frame. See U.S. Pat. No. 1,938,157.
A bicycle transmission having a steering lever provided with a number of levers connected to and operated by each other through suitable gearing is also known. The levers communicate with rotary movement to a connect a central shaft from which the axle is driven. See, U.S. Pat. No. 397,144.
A bicycle transmission with a shiftable gear drive arrangement combined with a chain to connect a rotary power input to the driven wheel is also known. A two-speed arrangement is illustrated. A lever slides a gear assembly between two different positions on a shaft to provide the two operating speeds. See, for example, British Patent No. 25,975.
Of course, drive gear transmissions are also generally known for use in a tricycle. Such a transmission can include an element constructed from a pair of gear wheels on a common shaft.
Other patents related generally to bicycle transmissions are also known, see, for example, U.S. Pat. Nos. 222,779; 283,697; 573,285; 668,784; 881,729; 1,332,709; 2,518,537; 2,687,897; 4,077,648; German 72,199; and French 541,261.
None of those known transmission assemblies however provide the broad range of gear ratios needed for current recreational and competitive cycling. Moreover, the known transmission assemblies do not take advantage of the enhanced driving power available from a cranking mechanism which is eccentrically positioned relative to the transmission input axis so as to ergonomically power the transmission.
A general object of the present invention is to provide a bicycle transmission having multiple gear ratios and providing a direct driving connection between a power input and the driven wheel.
A more particular object of the present invention is to provide a bicycle transmission having multiple gear ratio controls each providing multiple gear ratios so as to increase the range of gear ratio connections between the input shaft and the driven wheel of a bicycle.
A further object of the invention is the use of an eccentrically powered crank assembly in connection with a multi-speed bicycle transmission. The eccentrically powered crank assembly is operative to make efficient use of the torque and power available from a person operating the bicycle.
A bicycle transmission which satisfies these and many other advantages includes a gear train connected to an over-running clutch on a driven wheel of a bicycle. The gear train of the transmission includes multiple gear shifting devices, each of which is capable of changing the gear ratio of the transmission through several speed changes determined by the ratios of the gears on the associated sprocket.
The gear shifting devices can include a shaft directly connected to a shaft carrying a spur gear in the transmission. By moving the shaft vertically upwardly, the associated spur gear moves between several different positions in driving relationship with portions of a corresponding sprocket, each of which corresponds to a different gear ratio. The shaft can also be manipulated to move the spur gear downwardly to reverse the gear ratio change by moving it laterally and pushing downwardly until the appropriate gear ratio is obtained.
The gear shifting device can also include corresponding cable pull arrangements attached to a corresponding spur gear in the transmission. By pulling up on the cable, the associated spur gear moves between several positions in driving relationship with a portion of the corresponding sprocket. By biasing the spur gear toward its initial, lowermost position, releasing tension on the corresponding cable allows the corresponding spur gear to move to the gear ratio associated with the lowermost sprocket position.
Another important part of the invention concerns the cranking mechanism used to power the direct-drive transmission. More particularly, the cranking mechanism is arranged to be eccentrically driven. This eccentric driving relationship is obtained through use of driven, telescoping cranks on either side of the bicycle, one for each foot. The telescoping cranks are driven to extend the radial distance between the cranking axis and the pedal during a forward portion of the pedal orbit and are also driven to reduce the radial distance between the cranking axis and the pedal during a return portion of the pedal orbit. In this manner, the pedals traverse a pedal orbit which is eccentric to the axis of the input to the bicycle transmission. Moreover, the pedal position uses the power available from leg extension to drive the bicycle transmission while minimizing the power input as the leg bends backwardly at the knee. Thus, an ergonomically arranged pedal cranking mechanism is provided.